1. Field of the Invention
The present invention relates to a metal nozzle boss which is combined with a plastic liner of a composite vessel preferably used as a high-pressure vessel.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
In recent years, to produce a high-pressure composite vessel, preferably used as a fuel tank of natural gas vehicles or a hydrogen tank of fuel cell vehicles, a plastic liner must be first shaped using polymer resin, such as HDPE (high density polyethylene). Thereafter, carbon fiber or glass fiber, impregnated with thermosetting polymer resin, such as epoxy resin, is wound around the plastic liner, thus providing a light high-pressure composite vessel. During the process of producing the light high-pressure composite vessel, a metal nozzle boss is inserted into an end of the plastic liner and is combined with the end of the liner, so that a regulator or valve can be coupled to the end of the high-pressure vessel by means of the nozzle boss.
In the related art, a heavy high-pressure composite vessel, comprising a metal liner and carbon fiber or glass fiber impregnated with thermosetting polymer resin and wound around the metal liner, has been proposed and used. However, in recent years, to produce a light high-pressure vessel which can reduce the time required to inject gas into the high-pressure vessel, a high density polyethylene plastic liner is shaped through injection molding or rotary molding and, thereafter, carbon fiber or glass fiber, impregnated with epoxy resin or polyester resin, is wound around the plastic liner, thus providing a light high-pressure vessel. The conventional composite vessel having a metal liner is problematic in that the vessel is heavy, easily corroded and has increased production cost. However, the composite vessel having a plastic liner is advantageous in that the vessel is light and can effectively resist corrosion and fatigue caused by repeated injections of gas into the vessel, and the vessel reduces the time required to inject gas into the vessel. Thus, in recent years, various composite vessels having plastic liners have been actively studied and proposed. However, the composite vessels using plastic liners are problematic in that adhesion strength at the junction between the plastic liner and the metal nozzle boss is reduced. In an effort to overcome the above-mentioned problem of reduced adhesion strength, Korean Patent Laid-open Publication No. 2003-0041002 (Laid-open Publication Date: May 23, 2003) discloses a method of securely combining a metal nozzle boss with a plastic liner of a composite vessel by providing a fine uneven surface on a predetermined surface of the metal nozzle boss, by treating the uneven surface of the nozzle boss using a plasma, by coating a thermosetting adhesive on the plasma-treated uneven surface, and thereafter, by forming a plastic liner combined with the metal nozzle boss through an injection molding process in which the metal nozzle boss is heated and inserted into the cavity of a mold and placed at a predetermined position in the cavity prior to injecting resin into the cavity.
Furthermore, when a metal liner is used in a composite vessel, the metal liner is integrated with a metal nozzle boss so that gas does not leak through the junction between the metal liner and the metal nozzle boss. However, when a plastic liner is used in a composite vessel, gas may leak through the junction of the metal liner and the metal nozzle boss due to delamination of the junction. The delamination of the junction between the metal liner and the metal nozzle boss of a conventional composite vessel is caused by the low surface energy of the plastic liner or by a reduction in elasticity of the plastic liner material due to repeated injections of gas into the vessel over a lengthy period of time. In the prior art, to prevent the gas leakage through the junction between the plastic liner and the metal nozzle boss of the conventional composite vessel, the junction may be chemically processed or may be coated with an adhesive, or the metal nozzle boss may be physically configured such that the boss can be securely combined with the plastic liner.